1. Field of the Invention
The present invention relates to electrical machines generally, and more specifically to rotor assemblies for electrical machines.
2. Description of the Related Art
The rotor assembly of an automobile alternator of the "claw pole" variety generally comprises two opposing "claw pole" pole pieces with intermeshing fingers. The two "claw pole" pole pieces define an inner space in which is disposed a field coil assembly.
The field coil assembly normally comprises a bobbin around which is wound a coil of wire. The field coil assembly is then affixed to the two "claw pole" pole pieces for rotation therewith.
In order to maximize the power output capability of an alternator, it is advantageous to incorporate as much wire into the field coil assembly as possible, to maximize the electromagnetic field generated by the field coil. However, maximizing the amount of wire can cause two problems. First, the wire can tend to "spill" out of the bobbin as the rotor rotates during operation of the alternator. Second, the wire can tend to short-circuit against the inner radius defined by the pole fingers of the two "claw pole" pole pieces.
One solution to the two problems is the incorporation of flaps which project radially outward from the walls of the coil bobbin. Typically, each wall of the bobbin would have as many flaps as the number of pole fingers on one "claw pole" pole piece. The flaps on each wall of the bobbin would further be disposed such that they would each be bent over the field coil by one pole finger of a "claw pole" pole piece when the rotor were assembled. The flaps thereby bent over help eliminate the two problems referenced above which are encountered when trying to maximize the wire in the field coil of the alternator. Specifically, the flaps when bent over help retain the field coil wire in the bobbin. Also, the flaps provide an electrically insulating barrier between the coil wire and the inner radius defined by the pole fingers of the two "claw pole" pole pieces.
Although the bobbin flaps are quite effective in eliminating the two above-referenced problems, the flaps introduce one problem of their own. Because the flaps are bent over by pole fingers of the "claw pole" pole pieces, alignment between the pole fingers and the bobbin flaps must be maintained as the rotor is assembled. Because the bobbin flaps normally have significant stiffness, such alignment is often hard to maintain. The result is a rotor assembly process which can be difficult.
Therefore, a rotor which is designed to facilitate alignment of the pole fingers with the bobbin flaps will provide advantages over the prior art. Specifically, assembly of such a rotor will be made considerably easier.